This is a request for a shared Laser-Scanning confocal imaging system, a powerful new development in fluorescent and interference contrast microscopy. It utilizes a computer-controlled mirror- scanning system to rapidly deflect a sharply-focussed, diffraction- limited laser beam point by point through a horizontal (x,y) 'optical-section' of a living cell or thick specimen. using confocal imaging, computer-aided image construction and a sensitive, photomultiplier detector, it generates a very shallow depth of focus (0.7 um) and unprecedented lateral resolution (0.2 um, exceeding the limit of resolution in a light microscope), with marked diminution of optical noise (glare) in the plane of focus. Using a step-motor, it is possible to to acquire 3-dimensional subcellular maps of molecular distributions and molecular activities in living cells for dynamic studies of rapidly occurring intracellular events. This request is being submitted by a group of 14 NIH-funded investigators from the department of Cell Biology, Pathology, Biology and Internal Medicine at the Yale University School of Medicine. The use of the instrument will be controlled by an Internal Advisory committee. The instrument will be housed in the Liver Center and operating costs will be defrayed by charging hourly User's fee. Additional core equipment is being made available by the liver Center. The major applications of the instrument will be: 1) Studies of structural cell biology with 3-D distribution and co-localization of fluorescent probes and macromolecules in fixed tissues and live cells; 2) Studies of cellular physiology, including 3-D subcellular distributions of calcium, pH and organic ligands using fluorescent labels and studies utilizing confocal differential interference contrast microscopy for 3-D reconstruction and quantitation of volumes of cells and interspaces (canaliculi) using microscopic optical planimetry.